This report summarizes the efforts of 53 nations to improve global nuclear security from 2010 to 2016. The Nuclear Security Summit, sponsored by the Arms Control Association and the Partnership for Global Security, convened four meetings of world leaders and resulted in regular, voluntary commitments to reduce the threat of nuclear and radiological terrorism. The Summit's accomplishments include the recovery or elimination of more than 1,500 kilograms of highly enriched uranium (HEU) and plutonium, the establishment of training and support centers, and updates to national laws on nuclear safety and security by member nations. Prepared for the final 2016 meeting of the Summit, the report includes detailed information on actions by each participant country to increase nuclear security. The actions are organized into five categories: nuclear and radiological security; counter nuclear and radiological smuggling; education and training; governance structures and processes; and joint statement participation.